The present invention relates to electrical motors and, more particularly, to a reversing mechanism for motors particularly motors used in portable electric tools.
In portable electric tools such as portable drills, screwdriver/drills and screwdrivers, it is desirable to reverse the direction of rotation of the motor to facilitate, for example, the loosening and removal of screws, the removal of the drill bit from a hole, or the removal of a thread cutting tool out of a bore after cutting a thread in the bore by reverse rotation of the cutting tool.
One conventional method for reversing universal motors is to reverse electrical connection of the brushes and stator windings. To obtain optimum performance and maximum brush life in a reversing motor, there must be a compensation mechanism for the distribution in the magnetic field called neutral plane shift that results from the interaction of the rotor and stator fluxes. One such mechanism is shifting of the brush location about the armature axis in the direction that is opposite to the direction of rotation of the armature. Such shifting avoids sparking and excessive brush and commutator wear. In addition, the sparking will cause electrical noise to be transmitted into the power source supplying electrical energy for the tools. One such brush shifting and reversing switch assembly is disclosed in U.S. Pat. No. 5,089,729 which is assigned to the assignee of the present invention. Here, the assembly includes a reversing switch and an actuator which is movable between forward and reverse positions to reverse the connections of the reversing switch to reverse the direction of the motor rotation. The actuator has a sleeve connected to the reversing switch and surrounds the motor stator to guide movement of the actuator between the forward and reverse positions. A manual tab is located in the motor housing slightly forward to a manual power switch in the tool handle. While this assembly works satisfactory for its intended purpose, designers strive to improve the art.